The objective in breeding the present novel variety, assigned the denomination MOR, was to obtain a late ripening mandarin citrus wherein the fruit has few seeds.
The breeding program of the Agricultural Research Organization, the Volcani Center, Bet Dagan, Israel includes, in addition to performing various cross pollinations, inducing seedlessness by mutation breeding in easy peeling varieties.
In the spring of 1985 about 400 buds of an easy peeling mandarin cultivar, Murcott, was irradiated at the Nahal Soreq Nuclear Center, Yavne, Israel, by exposure to 35 kh of gamma radiation from a .sup.60 Co source. Sour Orange nucellar rootstocks were bud grafted with the individual buds of irradiated Murcott budwood and labeled mV.sub.1. Six to nine months after grafting the irradiated budwood, individual buds from the mV.sub.1 plants were regrafted on Sour Orange nucellar rootstocks to establish about 700 mV.sub.2 plants.
Field plantings were established from container grown mV.sub.2 plants in the spring of 1987. The first fruits were observed in January-February 1989 and a second observation of the fruits was made in January to February 1990.
One of the selections, which was designated 13/24, had medium to large sized orange colored fruit, and was easy to peel. This selection was distinguished from Murcott by the following features.
The selection 13/24 was a compact tree. During the four years after being transplanted to the grove it was consistently 1/3 to 1/2 the size of Murcott.
Selection 13/24 had fruit with few seeds. Typically, this selection had fruit with 5-7 seed per fruit as compared with 20-25 seeds per fruit for Murcott.
Selection 13/24 has flowers with low pollen fertility. Typically, 28-30% of the pollen grains of selection 13/24 were stained by acetocarmine as compared with 95% staining for Murcott.
The occurence of a favorable selection such as `13/24` from a limited population was surprising since the mutation frequency would be expected to be low, about one in 10,000 to about 1 in 100,000 and deleterious mutations can also occur.